<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    header {
      height: 60px;
      width: 100%;
      background: #ffd34e;
    }

    footer {
      height: 100px;
      width: 100%;
      background: rgb(210, 209, 208);
    }

    .content {
      overflow: hidden;
    }

    .main {
      float: left;
      width: calc(100% - 400px);
    }

    .left {
      float: left;
      width: 200px;
      height: 500px;
      background: rgb(131, 124, 104);
    }

    .right {
      float: left;
      width: 200px;
      height: 500px;
      background: rgb(131, 124, 104);
    }
  </style>
</head>

<body>

  <div class="content">
    <div class="left">左侧栏</div>
    <div class="main">主要内容</div>
    <div class="right">右侧栏</div>
  </div>
  <footer class="footer">底部</footer>

  <div class="cell border-1px"> cell </div>
  <div class="cell border-1px-top"> cell </div>

  <style>
    .cell {
      width: 100px;
      height: 100px;
      position: relative;
    }

    .border-1px::after {
      content: '';
      position: absolute;
      box-sizing: border-box;
      top: 0;
      left: 0;
      width: 200%;
      height: 200%;
      border: 1px solid #000;
      border-radius: 4px;
      -webkit-transform: scale(0.5);
      transform: scale(0.5);
      -webkit-transform-origin: top left;
    }

    .border-1px-top::before {
      content: "";
      position: absolute;
      top: 0;
      left: 0;
      right: 0;
      border-top: 1px solid red;
      transform: scaleY(.5);
      transform-origin: left top;
    }
  </style>


</body>

</html>